Garden Detective: Avoid using pesticides for aphids

In the past, you wrote about using Bayer Advanced Tree and Shrub Insect Control between Jan. 15 and Feb. 15 to control aphids on trees for a full year. We have a major problem each summer on our crepe myrtles. Bayer is very expensive and I’ve heard there is a cheaper but equally effective alternative brand. Do you happen to know about it?

– Linda Mason, Sacramento

According to UC master gardener Veronica Simpson, the active ingredient of Bayer is imidacloprid. Systemic insecticides are also available for aphid management, primarily for woody ornamentals. These materials, including imidacloprid, are very effective and are especially useful for serious infestation of aphids such as the woolly hackberry aphid, which often is not effectively controlled by biological control or less-toxic insecticides.

But imidacloprid can have negative impacts on predators, parasitoids and pollinators, especially bees. So its use should be avoided where soaps and oils will provide adequate control. To protect pollinators, don’t apply imidacloprid or other systemic insecticides to plants in bloom or before bloom.

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Consider these alternatives to chemicals: Checking your trees regularly for aphids, at least twice a week when growing rapidly and the temperatures are warm, will help to catch the infestations early.

Knocking them off with a strong spray of water will dislodge aphids. Using the water sprays early in the day will allow plants to dry and be less susceptible to fungal diseases. A mixture of 2 to 3 tablespoons of dish soap (such as Ivory) to a gallon of water makes an effective spray.

Insecticidal soap, neem oil and narrow range oil provide temporary control (only killing aphids present on the day they are sprayed) if applied thoroughly to infested foliage. Target the underside of leaves as well as the top. Do not use soaps or oils on water-stressed plants or when the temperature exceeds 90 degrees.

Each summer, we have a number of fully loaded fruit trees (apple and pear) that we would like to harvest and donate fruit to our church’s “feed the homeless” program, but I am afraid to offer them because the trees are in close proximity to our septic drain field, and we are afraid of contamination of the fruit that would cause problems. Do you think we should just destroy our crops or would the fruit be OK to offer to the program?

– Richard Gunsaullus,

West Sacramento

According to UC master gardeners Carol Hunter and Mary Griggs, it depends on the distance of the trees from your leach field.

You do not say how close the trees are to your leach field. However, information from UC Cooperative Extension as well as Virginia, Washington and Nevada Cooperative Extensions indicate that if at all possible, use your septic drain field for ornamentals and plant your fruits and vegetables elsewhere. They also do not recommend construction of raised beds over the field; they might inhibit evaporation of moisture from your leach field.